Generally, a copper alloy casting is used for a water contact metal fitting. For such a copper alloy casting fitting, it is ideal that a copper alloy having excellent machinability, strength, corrosion resistance, and castability be used as the structural material thereof.
In addition, bronze alloys such as CAC406 of JIS H5120 or the like are well known as a copper alloy having excellent machinability or the like.
However, the above alloys contain a large amount of Pb (4 mass % or more) to secure machinability. Pb is a harmful substance having a negative influence on human body and environment, therefore, in recent years, the usage of Pb has been strictly restricted. For example, when an operation in hot environment is performed such as melting, casting or the like of an alloy containing a large amount of Pb, the metallic vapor generated does harm to a human body and causes environmental contamination because such vapor comes to contain Pb. In addition, when an alloy containing a large amount of Pb is used for a water faucet, a valve or the like, Pb can be eluted due to the contact with potable water or the like.
Furthermore, the properties of the aforesaid bronze alloys such as strength, corrosion resistance, castability or the like are far from satisfactory.
Even in the related art, it is well known that grain refinement is extremely effective in improving the machinability, castability or the like of a copper alloy casting by removing dendrite structure, a typical structure of a casting.
Basically, the grains of a copper alloy are refined as follows: (A) the grains are refined during the melt-solidification of a copper alloy, or (B) the grains are refined by deforming such as rolling or the like, or by heating the melt-solidified copper alloy (ingot such as slab or the like; casting such as die casting or the like; molten casting products or the like), in which stacking energy such as distortion energy or the like acts as a driving force. In both cases, Zr is known as an element contributing to the grain refinement effectively.
In the case of method (A), since the grain refining effect of Zr during melt-solidification depends considerably upon the other elements and the contents thereof, the grains cannot be refined as much as desired. Consequently, method (B) is widely used, and the grains are refined by heating and then deforming a melt-solidified ingot, casting or the like.
JP-B-38-20467 discloses that the grains can be refined further as the content of Zr increases, on the basis of the measurement results that the mean grain size of a copper alloy containing Zr, P, and Ni, on which solution treatment and subsequent cold-working at the working rate of 75% are performed, is 280 μm when no Zr contained, 170 μm when 0.05 mass % of Zr contained, 50 μm when 0.13 mass % of Zr contained, 29 μm when 0.22 mass % of Zr contained, and 6 μm when 0.89 mass % of Zr contained. In addition, JP-B-38-20467 proposes that the content of Zr should be in the range of 0.05 to 0.3 mass % in order to avoid a negative influence caused by the excessive content of Zr.
Furthermore, JP-A-2004-100042 discloses that the mean grain size can be as fine as about 20 μm or less if a copper alloy, to which 0.15 to 0.5 mass % of Zr is added, is solution-treated and deformed after casting.                Patent Document 1: JP-B-38-20467        Patent Document 2: JP-A-2004-100042        
However, if a casting is heated and deformed to refine the grains like method (B), the manufacturing cost rises. In addition, a deformation process for distortion is not always available depending on the shape of a casting. Therefore, it is preferable that the grains are refined while a copper alloy is being melt-solidified by method (A). However, as described earlier, in the case of method (A), since the grain-refining effect of Zr considerably depends on the other elements and the contents thereof during melt-solidification, the grains cannot be refined as much as expected even when the content of Zr increases. In addition, since Zr has an extremely strong affinity to oxygen, when Zr is melted and added in the air, Zr is likely to be oxidized, and thus the yield of Zr decreases drastically. As a result, even when an obtained casting contains a little amount of Zr, a considerable amount of Zr needs to be charged upon pouring. On the other hand, if too much oxide is generated during melting, the oxide can be included into a molten alloy during pouring, thereby inducing casting defects. In order to avoid the generation of the oxide, it can be considered that the raw materials are melted and cast under a vacuum or inert gas atmosphere; however, this method raises the manufacturing cost. Furthermore, since Zr is an expensive element, it is preferable that the adding amount of Zr be suppressed as low as possible from an economic viewpoint.
Consequently, it is demanded that the content of Zr be made as low as possible and a copper alloy casting, the grains of which are refined at the stage of melt-solidification during casting, be developed.